Absorbent planar structures are well-known as wiping cloths for household use. Because of their absorbency, they may be called "sponge cloth". Various kinds of sponge cloth are known, the most popular variety being the viscose sponge cloth. Other kinds include rubber or polyurethane sponge cloths which have achieved no parctical significance. In addition to the above-mentioned sponge cloths, there also exist sponges and window cloths made of cross-linked polyvinyl alcohol, which are used to a small extent. All the above-described products, especially the cloths or sponges containing cross-linked polyvinyl alcohol, are hard and brittle in their dry state.
As already mentioned, the so-called viscose sponge cloth is in common use. Such cloth often contains a woven fabric in order to increase its tear strength. Since it is also hard and brittle in its dry state, viscose sponge cloth may be impregnated with a dilute softener solution, e.g., glycerin, in order to eliminate its stiff feel. Viscose sponge cloth without such a softener additive cannot withstand any mechanical stress in an absolutely dry condition. Also of note is the fact that cloth without a softener absorbs only about 10% moisture when climatized, while a "softened" cloth absorbs about 20% moisture. Thus, in use, a softened cloth which has been merely air-dried may be subjectively perceived as dry but in fact will still contain 15 to 20% moisture. The result is that the cloth does not become completely brittle. Despite the softening, the cloth's feel is still not soft and pleasant, nor can the waviness of the cloth material be completely eliminated. Rather, as it dries, the cloth will tend to arch mainly at the corners such that planar contact is no longer maintained. For the above-stated reasons, the viscose sponge cloth is usually packaged moist so as to avoid such problems. However, this poses hygienic problems associated with bacterial and fungal growth, which may require the addition of bactericides and fungicides.
"Softening" with glycerin or other water-soluable substances is also highly disadvantageous because the "softeners" are washed out during use so that the originally soft sponge cloths become hard and stiff again when dry. Therefore, although softened cloths may have the advantage of a high absorption rate and great water absorbing capability, as well as a pleasant feel in a moist condition, such advantages are countervailed by the disadvantage of poor durability, especially at the surface. Wiping until dry is not possible, and in spite of being packaged with softeners, the cloth, when in dry condition, becomes hard and stiff again with use. And, of course, the danger of bacterial and fungal growth must always be reckoned with. Moreover, when such softened cloths are manufactured according to the well-known cellulose xanthogenate method, more or less severe environmental pollution results.
As a consequence of the above-described state of the art, it is an object of the present invention to provide an absorbent planar structure which absorbs great amounts of water quickly without the known disadvantages associated with the viscose sponge cloth. A cloth produced according to the present invention should be soft and have a pleasant feel even in its dry state. It also should not exhibit bacterial and fungal growth. Furthermore, cloth according to the present invention is characterized by the fact that softeners, pore formers or similar substances which interfere with and change the properties of the cloth during use, are eliminated. Also, it is an object of the present invention to provide an environmentally safe method of producing novel "sponge cloths" of the present invention.
The above-cited objectives are satisfied by the absorbent planar structure, and method of manufacturing same, as are described in the accompanying claims.